Someone seems to have put usefully the pretty accurate alignment of lines, including station platform positions and even lengthy interchange passages such as the one at Green Park the length of Arlington Street, on Open Streetmap.
This, among others, correctly shows the Moorgate to Finsbury Park line, mentioned above, as taking a direct line north of Old Street. The penetration accident there surprised me too, as I had always thought that, like other old tube lines, it was under the main road, which is only fractionally to the east, and any direct drawing (which is how it actually is) was just inaccurate cartography.
It had somewhat fallen into an administrative void, as the line was transferred from the Underground to BR in 1976, the Underground had thus subsequently removed it from their asset mapping whilst the BR detail had been drawn up before the transfer.